The overall goal of this project is to elucidate mechanobiological mechanisms and consequences of functional deterioration of articular cartilage, leading to partial-thickness erosions in the human knee in aging and osteoarthritis. Biomechanical abnormalities occur in the superficial zone of articular cartilage during normal aging, and this is associated with an increased incidence of osteoarthritis. The overall hypothesis is that the superficial zone of normal human knee articular cartilage undergoes aging-related mechanobiolgoical decompensation due to both cell and matrix dysfunction, with a resultant compromise in both cartilage lubrication and load-bearing properties. To address this hypothesis, we propose to test the following aims: 1) Analyze human and mouse knees for spatial signatures of biomechanical dysfunction or failure of the articular cartilage, and the relationship of such variation to putative determinants, matrix composition and structure and also cell organization and phenotype; 2) Determine if in vitro dynamic loading of cartilage explants in compression and shear cause cell responses and matrix remodeling in the superficial zone that lead to aging-related compromise of cartilage lubrication and load-bearing functions.